Caravan

From what Alex read about the barrier formations during his time in the library, he remembered there being written that one could destroy a barrier if they used a particularly strong attack on a weak point. 

There were various ways to find the weak point of a barrier and what he had just done was one of them. 

Barriers that were not sturdy made a lot of fluctuations on the surface when attacked and sometimes showed imperfections. One had to have really good knowledge about the barrier or barriers, in general, to be able to do this. 

Alex didn't know much about formations, in general, to know about barriers, but he did have information about the barrier through Zexi's notes. According to the note, if the barrier had low efficiency, it could be destroyed in the same way Alex did. 

Once the formation had disappeared, Alex immediately stretched his spiritual sense to the 35-meter distance so he could see everything just in case.